1. Field of the Invention
The present invention relates to an assay apparatus and sensor holding method. More particularly, the present invention relates to an assay apparatus and sensor holding method, in which a sensor unit can be positioned reliably without offset or change in moving a pipette device.
2. Description Related to the Prior Art
An assay apparatus for assay in utilizing attenuated total reflection is used for various kinds of studies in a biochemical field or the like, for example to study interaction of protein, DNA and various biomaterials, and to select candidate drugs by screening. Also, the technique is useful in the fields of the clinical medicine, food industries and the like.
A surface plasmon resonance (SPR) sensor is known as an assay apparatus in utilizing attenuated total reflection. Surface plasmon is a term to mean the compressional wave created on the surface of the metal and included in plasmon as quantized expression of the compressional wave. Free electrons in a metal vibrate to generate the compressional wave.
U.S. Pat. Nos. 5,164,589 and 5,313,264 (corresponding to JP-B 3294605) disclose an SPR assay apparatus with Kretschmann configuration. In the assay apparatus, the sensing surface is positioned opposite to an interface where a metal thin film is connected with a prism as dielectric block. Light is applied through the prism to the sensing surface. Total reflection of the illuminating light occurs. Reaction of samples is assayed by detecting the SPR on the sensing surface.
Biomaterials as samples are handled as sample fluid which contains a sample and fluid medium to which the sample is added, for the purpose of preventing modification or deactivation due to drying. Examples of fluid media include physiological saline water, pure water, buffer liquids and the like. The assay apparatus of U.S. Pat. Nos. 5,164,589 and 5,313,264 (corresponding to JP-B 3294605) is used to detect and study interaction between biomaterials. The flow channel is formed for flow of the sample fluid in contact with the sensing surface. A flow cell with a flow channel and the prism are disposed on an assay stage of the assay apparatus. A sensor unit of a chip type is set on the assay stage, having thin film of metal formed on a glass substrate.
In U.S. Pat. Nos. 5,164,589 and 5,313,264 (corresponding to JP-B 3294605), a pump is connected with the flow channel by a conduit, valve and the like, to supply the flow channel with the sample fluid from a fluid reservoir. However, a problem of contamination is likely to occur in that the sample may stick on the inside of the conduit and will mix with the sample fluid.
To solve such a problem, a type of the assay apparatus is suggested in which pipette devices are used. Each of the pipette devices includes a pipette head and a pipette tip secured to the pipette head removably. The pipette devices dispense the sample fluid into the flow channel. It is possible in the assay apparatus with the pipette devices to prevent contamination in introducing the sample fluid into the flow channel by replacing pipette tips each time that the fluid is changed over.
The sensor unit for use in the assay apparatus with the pipette devices includes a flow cell, the prism and a connection mechanism. The flow cell has the flow channel. The prism is overlaid with the thin film of metal. The sensor unit connects a flow cell with the prism by positioning the flow channel on the thin film. A flow channel is a conduit extending through a flow cell in an U shape. Orifices are formed at ends of the flow channel and open in the upside of the flow cell. A lower portion of the flow channel is open, and is closed by a thin film of metal. Therefore, fluid can contact the thin film on the flow channel by introducing the fluid into the flow channel. If a pipette device is used for dispensing the fluid into the flow channel, a tip of the pipette device is inserted in an end of the flow channel, so as to introduce the fluid being stored by aspiration in the pipette device.
However, it is likely in the assay apparatus with the pipette devices to create errors in measurement by incidentally shifting the sensor unit in loading or unloading the pipette devices on the flow channel. Such errors in the position of the sensor unit will change the position of the reflected light in the photo detector. Even if analysis according to a measuring signal and a reference signal is carried out, the error cannot be removed.
If a sensor unit is a multi channel type having a plurality of sensing surface and the flow channel associated therewith, samples on the sensing surfaces can be assay at the same time. However, the problem is further serious in high force exerted to the sensor unit upon loading and unloading the pipette device, because of the greater number of the pipette devices according to the number of the flow channel.